Electromagnetic induction apparatus and method of forming same



y 25, 1949- G. G. SOMERVILLE 2,477,350

. ELECTROMAGNETIC INDUCTION APPARATUS AND METHOD OF FORMING SAME FiledSept. 11, 1944 4 Sheets-Sheet 1 Inv ehbor: Gareth G. somerville,

l9 v H is Attorney.

y 1949- G. G. SOMERVILLE 2,477,350

ELECTROMAGNETIC INDUCTION APPARATUS AND METHOD OF FORMING SAME FiledSept. 11, 1944 4 Sheets-Sheet 2 "Fig.9.

Inventor Gareth G. Somer-ville,

H is Attorney.

July. 26, 1949- G G. SOMERVILLE 2,477,350

ELECTROMAGNETIC INDUCTION APPARATUS AND METHOD OF 'FORMING SAME FiledSept. 11, 1944 4 Sheets-Sheet 3 Inventor Gareth G. Somerville 175414476? JMZM -His Attorneg.

y 1949- s. G. SOMERVILLE 2,477,350

ELECTROMAGNETIC INDUCTION APPARATUS AND METHOD OF FORMING SAME FiledSept. 11, 1944 4 Sheets-Sheet 4 IHIHH III/IIHH IHHHH lhve hooi-z GarethG. Sorn'er'ville,

His Attorneg.

.Tatented July 26, I949 ELECTROMAGNETIC TUS AND METHOD New York muc'rion APPARA- or FORMING SAME Gareth G. Somerviile, Plttsfield, Mesa,assignmto General Electric Company, a corporation of ApplicationSeptember 11, 1944, Serial No. 553,523

Claims. ((31.175-356) My invention relates to electromagnetic inductionapparatus, to magnetic cores of the curved iron type, and to a method offorming the curved iron type core and producing an assembled magneticcore and winding for an electromagnetic induction apparatus.

Heretofore it has been customary to form electromagnetic inductionapparatus, particularly for application in low frequency or powerfrequency fields with magnetic cores formed of a plurality of assembledfiat punchings, or by fiatwise bending or winding a strip of magneticmaterial to produce a bent or wound core. In the high frequency fieldthe cores have been produced of powdered iron bonded together with asuitable binder.

A core formed of highly directional steel which is wound in the form ofa spiral so that the flux will pass along the most favorable magneticdirection throughout the entire periphery of the core will have a lowcore loss, and such a core has been used for some time in instrumenttype bushing current transformers since with this type of transformer itis not necessary to disturb the core to assemble it with the primarywinding as the primary winding usually includes a single conductor whichpasses through the ring shaped core, with a few turns of the secondarywinding distributed through and around the ring shaped c'ore. Also,although it has been known since the later part of the last century thatcores may be made of the flatwise bent type, for instance as shown inBritish Patent 7856 of 1889, it has been customary to form cores ofelectromagnetic induction apparatus by assembling the flat punchings,and apparently one reason for this was the clifiiculty which wasexperienced in assembling the annealed wound core with a preformedconductive winding structure without bending the magnetic materialbeyond its elastic limit, as bending beyond this limit destroys ordeteriorates considerably the magneticproperties of the steel.

In my application Serial No. 536,748, filed May 22, 1944, now Patent No.2,456,457, issued December 14, 1948, and assigned to the same assigneeas this present invention, I have described and claimed a curved irontype core for an electromagnetic induction apparatus which may beefficiently applied to a relatively wide range of transformers, andwhich includes a curved iron type core formed of at least two groups ofmagnetic sheets which have been precut to the desired size. The core isformed by assembling sheets of first one group and then from the otherso as to-produce a generally circular shaped core construction. Pressureis then applied to the inside and outside surfaces of the ring so as-tosuitably align the adjacent ends of the corresponding sheets from eachof the groups. The

core may then be expanded to the desired shape,

annealed, and after annealing one group is disassembled from the secondto form two core portions which portions may then be reassembled arounda preformed conductive winding structure.

It is an object of the present invention to provide an improved methodof forming a core of the above-mentioned type.

It is another object of my invention to provide an efllcient method ofproducing an assembled magnetic core and winding for an electromagneticinduction apparatus which is simple to practice and which will producean efiicient apparatus.

It is a further object of my invention to provide an electromagneticinduction apparatus having a core with an improved joint construction.

Further objects and advantages of my invention will become apparent fromthe following description referring to the accompanying drawing, and thefeatures of novelty which characterize my invention will be pointed outwith particularity in the claims annexed to and forming a part of thisspecification.

In the drawing Fig. 1 is a perspective view of an electromagneticinduction apparatus which is provided with an embodiment of myinvention; Fig. 2 illustrates two groups of sheets of magnetic materialwhich are employed to produce the cores of Fig. 1; Figs. 3 and 4illustrate steps of bending the sheets of the groups of Fig. 2; Fig. 5illustrates the groups of sheets having been assembled according to myinvention; Fig. 6 is a perspective view of the core of Fig. 5, and anexpanding mandrel; Figs. 7 and 8 illustrate the steps of forming thegenerally toroidally shaped core into a rectangular shaped coreconstruction; Fig. 9 illustrates the apparatus of Fig. 1 with one of thecore members being assembled around one leg of the conductive windingstructure, and the other core in the process of being assembled; Fig. 10illustrates another method of assembling the sheets around a windingleg; Fig. 11 illustrates a core construction which is provided with amodification of my invention; Fig. 12 illustrates in perspective twogroups of magnetic sheets which are employed in the core of Fig. 11;Fig.

13 illustrates one of the. sheets of the group of Fig. 12 after it hasbeen given a bending operation; Fig. 14 illustrates a core having beenassembled from the groups of. lamination's' illustrated in Fig. 12; Fig.15 illustrates somewhat diagrammatically a plurality of cores of thetype illustrated in Fig. 11 being assembled in an oven for a strainanneal treatment; Fig. 16 illustrates cores of the type shown in Fig. 11being assembled around the winding legs of a conductive windingstructure; Figs. 17 and 18 illustrate modifications of the coreconstruction illustrated in Fig. 11; Fig. 19 illustrates two groups ofsheets used in forming the core of Fig. 18; and Fig. illustrates amodified method of assembling'oores 01' the type illustrated in Figs. 11through 18 with a conductive winding.

Referring to .rlI. r of the drawing. I have illustrated anelectromagnetic induction apparatus having a preformed coil winding iwith two similar cores 2 and I surrounding legs s and I rebutt oint. butit will be understood as the descriptlon proceeds, that any suitabletype ioint construction may be produced according to my improved method.Although two cores are shown as linking a single conductive windingstructure it will be understood that my improved method may be user toform any suitable number of core members assembled with any suitablenumber of conductive winding structures, and to produce any suitabletype of electromagnetic induction apparatus, such as a transformer or areactor. Furthermore,.my invention may be used to produce anelectromagnetic induction apparatus for a wide range of sizes andapplications, such as cores employing relatively thin magnetic strips toproduce relatively small transformers for high frequency applications,the cores using relatively thick strips for the large type transformers.

' In order to produce thevcore illustrated in Fig. 1, I provide twogroups of magnetic sheets 0 and iii. as shown in Fig. 2. These sheets ofmagnetic material may be formed of any suitable material such as highlydirectional strip steel having the most favorable magneticv directionrunning longitudinally of the sheet. The two roups 9 and ill of magneticsheets have approximately the same number of sheets, and the sheets havesuch length so that corresponding sheets from each of the groups whenassembled will have a total length approximately equal to the peripheraldistance around the core at that particular layer in the finished core.Of course, they may have any other suitable length. Thus given the sizeof the finished core the designer can calculate the lengths of each ofthe sheets of the two groups which will be used to form the finishedcore. It will also be seen that by the use of the various combinationsof lengths of sheets of the two groups, any suitable type of scarfed,butt. or overlapped Joint may be provided as will be brought out moreclearly below.

In the production of the overlap 'scarfed butt joint, as shown in Fig.1, and as indicated by the numeral 8, I provide the one group 9 witheach sheet having approximately the same length. The sheets forming thegroup lil. however, have progressively different lengths, the shortestlength being used at the inner perimeter of the finished core and thecorresponding longer length being used toward the outer periphery. Themagnetic sheets may be cut to size in any suitable manner, such asmeasuring by hand and cutting to the proper size or they may be cut onmy improved index shearing machine. described and claimed in myapplication Serial No. 539,255,

filed June 8, 1944, now Patent No. 2,369,617, issued February 13, 1945,and assigned to the same assignee as this present invention. Such aningressively different lengths so as to produce the group is.Furthermore. openings or holes ii and it may be punched in each of thesheets as they are out. Theseholes may be punched in any suitable placein the sheets and in the two groups oi. sheets a and it the holes arepunched oil'set from the longitudinal center of each oithe sheets, aswill be seen in Fig. 2. It will be understood that the holes II and IImay be omitted if desired but these holes are used to facilitate theassembly of the sheets in the manner which, will be described below.

In order to assemble the sheets in the group! a and is, one sheet suchas sheet it from the group 8 may be passed through a plurality ofrollers H which are suitably set so as to give the sheet any suitableshape or set such as a substantially semicylindrical shape as isillustrated in Fig. 4. It will be understood that each of the sheetsfrom the group may be given a set in a similar manner and then assembledas is illustrated in Fig. 5. In order that the sheets will be assembledso as to provide a substantially closed core. one sheet from the groupit and one sheet it from the group in are assembled with their ends inabutting relation. In like manner a next sheet it from the group 8 isplaced adjacent the sheet l3. while the next adjacent sheet H from thegroup I0 is placed adjacent the sheet I! with the ends of the sheets l8and II in abutting relationship. It will be understood that one sheetfrom each group may be assembled at a time in the manner described aboveor a plurality of sheets such as 8 or 4 may be assembled together toform layers, each layer including a plurality of sheets from the samegroup.

In order to stagger the butt joints the sheets are assembledlongitudinally displaced so that the joint l8 between the sheets i3 andIt will not be in registry with the joint I9 between the sheets II andII. This may be accomplished in any suitable manner, and in theconstruction illustrated in the drawing this is obtained bylongitudinally reversing the adjacent sheets from the group. Thus, sincethe holes II and I2 are placed oi! center, when the sheet 18 isassembled by passing a pin 20 through the hole ii, the longer side ofthe sheet will extend either to the right or to the left of the pin andin the construction illustrated in Fig. 5 it will be seen that thelonger side of the sheet i3 extends to the right of the pin 20.Similarly the sheet I5 is assembled with a pin 2| passing through thehole I2 and with the short side of the sheet l8 extending to the rightof the pin and the longer side to the left of the pin 2!. In assemblingthe sheet it, however, the pin 2a is passed through the hole Ii with thelonger side extending in the opposite direction from the sheet l3. or tothe left, while the sheet i1 is assembled with the pin 2i passingthrough the hole l2 with the short side of the sheet if extending to theleft of the pin. By assembling the sheets in this manner it will be seenthat the joints of adjacent layers are staggered and such a method ofassembling magnetic sheet is described in further detail and claimed inmy above mentioned application Serial No. 536,748.

Furthermore, since the sheets before they are assembled are given apermanent set with a substantially semicircular configuration, it willbe apparent that the sheets will stand by themselves without assemblingthem in a form or ring. Therefore this facilitates the assembly of thesheet so that the sheets may be stacked from dex shearing machine willproduce sheets of prothe inside out to produce the toroidally shapedfiguration they are to aeraesc construction as is seen that bands 23 areprovided around the outer periphery and which are spot welded at 24.When the wedge shaped portion 25 or the expansion mandrel 22 is forcedinto the mandrel, it will be apparent that the core will be forced toassume a generally rectangular shape. However, the use of such anexpansion mandrel may break the joints apart at l8 and I 9 as well asthe other joints so that it is desirable to apply pressure to theoutside surfaces of the core in the manner illustrated in Fig. 7. Thusthe core may be placed on a suitable base and a piston 26 pusheddownwardly to force the core to more closely assume the shape of themandrel. Relatively movable pistons 21 and 28 may also be applied forapplying force in a plane at right angles to the force applied due tothe movable piston 26. when the core has the desired shape it may beheld in that position through a support which includes plates 29 and 3029 and 36, the core may be given a suitable strain relief anneal so asto give the various sheets a permanent set in their desired relativepositions and so as to also remove any deleterious strains.

After the core has been removed from the it is in condition to beassembled as that illustrated in Fig. 1, Thus as is illustrated in Fig.9 the core portions 6 and 1 are disassembled and reassembled around oneleg d of the conductive winding structure. On the right hand side ofFig. 9 there is illustrated one of the U-shaped core portions assembledaround the other winding leg and the other core portion in the processof being assembled. In order to hold the various laminations in theirdesired position it will be seen that suitable rivets 32 are provided inthe holes and H' which are used to facilitate the assembly of thesheets.

It will be understood that the joints may be placed in any suitableposition around the periphery of the core,.and when the joints areplaced in the legs, as is illustrated in the construction of Figs. 1 and9, the U-shaped core portions 8 and 1 are assembled by pushing themtogether in a direction generally parallel with the plane of the sheetin the legs.- In order therefore to facilitate the 4 of coilconstruction such for each layer, each sheet having about l6 milthickness, the sheets will return to their des red positions in assemblyin the manner shown in Fig. 9.

I When it is desired to employ a fewer number of sheets in each layerthan may be efiiciently assembled as shown in 9 by introducing theU-shaped portion E as a unit to fit with the U- shaped core portion 1, afew sheets-at a time 10 may be introduced in the manner illustrated into have the overlap butt joints as near the end of the winding window asis possible so as to facilitate the assembly of each of the sheets.

In Fig. 11 I have illustrated another type of trated in Fig. 12. The

of that layer. It will therefore be seen that adjaof the sheets 39 and40,- are placed in substantially abutting adjacent layer which is madeup 01' the sheets 4| and 42 are so assembled that ends 54 and}! whichare adjacent the overlapping ends I and 8 are placed in abuttingrelation while the opposite ends 58 and 81 are placed in overlappingrelation. With such a Joint construction adjacent ends of sheets oi eachthe layers will be in abutting relation while other adjacent ends willbe placed in overlapping relation.

Alter the sheets have been assembled to produce a generally toroidallyshaped core as is illustrated in Fig. 14 by assembling the sheets fromthe inside layer to the outside layer. the core may be annealed in thiscondition ii, a circular core is desired in the finished apparatus. orthe core may be expanded into a rcctangularly shaped core in the mannerdescribed above in connection with Figs. 8. 'I, and 8. The core to Jointmay be formed in any other suitable manner. if desired. It will beunderstood. however. that since every other joint in each 0! the yokeshas sheets in overlapping relation the joints are in effect sell lockingso that an expanding mandrel 22 may be employed to produce arectangularly shaped core and the joints will not pull apart as they mayin the construction as is illustrated in Fig. l. The cores may then begiven a strain relief anneal by stacking in an even as isdiagrammatically illustrated in Fig. 15. A suitable weight 58 may beplaced on top of the cores so that the winding leg portions of the corewill be relatively tightly compressed. and the resultant eicctromagneticinduction apparatus will therefore have a high space factor.

In order to assemble the core constructions after they are removed fromthe strain relief anneal. as is illustrated in Fig. 15. the cores may bedisassembled so as to produce two U-shaped cores 58 and 60 as isillustrated in Fig. 16. The core 59 may then be passed through a windingwindow SI of a conductive winding structure 82, and reassembled with theU-shaped core portion it by pushing the endstogether in a generaldirection parallel with the plane of the magnetic sheets and the yokes.

In the construction illustrated in Fig. 16, it will be seen that twocore portions are placed around winding legs 63 and 64, and after theone core has been assembled around the winding leg 64 a second core maybe assembled around the windin leg 83. Since the window is already halffull. if the window has been so designed that the tinished core willsubstantially flll the winding window it will be understood that withthe construction as is illustrated in Fig. 16. the yoke would have to beslightly flexed so that it will pass through the space between the outerperiphery oi the core member 59 and the inner surface of the Winding leg83. In order to facilitate therefore the assembly of a U-shaped coreportion 66 approximately half of the sheets of the core portion 65 maybe first assembled without any substantial flexing oi the sheet. Theremaining half of the sheets which make up he U-shape core portion 65may then be -assembled by slightly flexing one end as it is passedthrough the remaining space. Thus. a sheet 88 will be passed through thewindow in the manner illustrated in Fig. 6 and one end 81 it will beunderstood will be slightly flexed in order for it to pass through therelatively small space. However. only a slight flexing need be producedand since only a relatively small portion of the total core is soflexed. it will be understood that only a minimum amount of deleteriousstrains will be produced in the finished core construction. After thecore portion 65 has been assembled with the produce this type oiconductive winding structure it may be reassembled with another U-shapedportion in the manner described above in connection with the U- shapedcore portion Bil.

I have found that a joint construction of the type illustrated in Figs.ll through 16 produces a very eillclcnt core construction. and I havetabulated below the core loss in watts per pound and exciting current inampere turns transiormer formed in the manner described above inconnection with Figs. ll through 16. and having such a Jointconstruction:

The above data were obtained from a 8 kv.-a. 120 volt. 72 turn windingtransformer having a core weight of 35.25 pounds and a mean length ofmagnetic path of 19.69 inches.

In Fig. 17 I have illustrated an electromagnetic induction apparatushaving a core structure with a butt overlap joint of the typeillustrated in Figs. 11 and 16 except that the Joints are so placed inline with opposite surfaces of the winding that the substantiallyL-shaped core portions may be assembled without flexing any of thelayers. Thus the core construction includes core portions 88 and 88which surround a leg ill of a conductive winding structure. One jointconstruction II is in line with the inner surface of the winding leg 10while another joint construction 12 is in line with the outer surface ofthe winding leg ll. Similar core portions 68 and 89' surround the otherwinding leg 10' and the core portions I and 68 are introduced into thewinding window from opposite sides. The core portions 88 and 69' maytherefore be assembled with the core portions 68 and 68'. respectively.by assembling a few layers at a time. It will be understood that in theconstruction illustiated in Fig. 1'7 a similar joint is provided asshown in Fig. 11. that is. in any one layer adjacent ends at Joint iiare in abutting relation while the opposite ends at Joint T2 are inoverlapping relationship.

I have found that a joint construction of the type illustrated in Fig.17 produced a very emcient core construction and I have tabulated belowcore lossin watts per pound and the exciting current in ampere turns perinch oi a transformer as is illustrated in Fig. 17:

Density in Exciting (-ur- (ore Loss Kilwlinospcr rent A. '1. Watts perSquare inch per inch Pound 80 0.93 0 50 1.08 0 56 m l. 35 0 64 DIS 1. 860. 74 3. (iii 0. 882 4. 95 l. 005

per inch or a 11 may be employed with any other type of coreconfiguration, and in Fig. 18 I have illustrated this joint as appliedto a U-shaped core with a removable yoke which is the same type ofconstruction illustrated in my copending application, Serial No.536,748, in Fig. 21 of that application. The core constructionillustrated in Fig. 18 includes a U-shaped core portion 13 and aremovable yoke portion 14, the core portion 13 having such aconfiguration that the joint will be in the same general plane as thewinding legs. Each of the layers of the core includes a sheet from onegroup 15 as is illustrated in Fig. 19 and another sheet from a group 16.The sheets may be assembled in any suitable manner such as according tothe method as is described in my above mentioned copending application.Thus a sheet 11 from the group 75 may be placed with an end 18 abuttingan end 79 of a corresponding sheet 80 of the group IS. The ends '18 andi9 will be placed in abutting relationship and their opposite ends 8|and 82 will be placed in overlapping relationship. In order that theadjacent sheets will have joints which are staggered, it will beunderstood that holes 83 are placed in the group of sheets 16 displacedfrom the longitudinal center line and by longitudinally reversingadjacent sheets in the manner described in my above mentioned copendingapplication. Serial No. 536,748,

the joints may be staggered to produce the core construction of the typeillustrated in Fig. 18.

In the constructions illustrated above, the

' cores have been assembled with preformed conductive windingstructures, while in Fig. 20 I have illustrated an arrangement forwinding a conductor on two U-shaped core members. Thus U-shaped coremembers 84 and 85 are provided with winding legs adjacent each other,and when the U-shaped core portions are rotated, a conductor 86 may bewound on the winding legs to produce a coil construction.

Although I have shown and described particular embodiments of myinvention, I do not desire to be limited to the particular embodimentsdescribed, and I intend in the appended claims to cover allmodifications which do not depart from the spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of producing an assembled magnetic core and winding for anelectromagnetic induction apparatus including the steps of providing twogroups of substantially straight sheets of magnetic material each havinga. length less than the total length of the perimeter of the finishedcore and with the sheets of at least one of the groups havingprogressively diil'erent lengths, individually fiatwise bending saidsheets into semi-cylindrical shape, and assembling the sheets from bothgroups beginning with the smaller sheets and using progressively longersheets to provide a closed magnetic core of a plurality of layers witheach layer including one sheet for eachgroup, giving the core the finalshape it will have in the finished apparatus, annealing in that positionand disassembling the groups of sheets into two core portions andassembling around a winding so that the sheets 00- cupy the samerelative position they had before disassembly without causingdeleterious strains in the core.

2. The method of producing an assembled core and winding for anelectromagnetic induction apparatus including the steps of providing twogroups of sheets of magnetic material each having a length less than thetotal length of the perimeter of the finished core and with the sheetsof one group having progressively different lengths and the sheets ofthe other group having approximately the same length, fiatwise bendingthe sheets of at least one group and assembling the sheets from bothgroups beginning with the smaller sheets and using progressively largersheets to provide a closed magnetic core of a plurality of layers andwith each layer including one sheet from each group with the adjacentsheets of each group having ends in substantially abutting relationship,annealing in that position, disassembling the groups of sheets into twocore portions and assembling with a winding so that the sheets occupythe same relative position as they had before disassembly withoutcausing deleterious strains in the core.

3. A laminated magnetic core having a joint extending entirely across asection of said core and extending but a relatively short distance alongsaid core, said core joint comprisin collectively individual joints inall the lamination layers at that part of the core, said individualjoints being alternate butt joints and overlap joints, said individualjoints being themselves in overlapping relation whereby a section of thecore through all of said butt joints has the same magnetic area as themain part of said core while being only fifty per cent thicker than themain I part of said core by reason of the double thickness of theindividual overlap joints in alternate layers.

4. A laminated magnetic core having a core joint consisting of as manysubstantially aligned lamination joints as there are lamination layers,said lamination joints being butt joints and overlap joints insubstantially equal numbers whereby the flux density in the core jointis substantially the same as in the core on both sides of the corejoint.

5. A closed laminated magnetic core having two lamination pieces perlayer, there being two joints in each layer between the ends of thepieces forming each layer, one joint in each layer being a butt jointand the other joint in each layer being an overlap joint, said jointsbeing oriented into two groups of adjacent joints with each groupforming a core joint which extends completely through the core, theindividual layer joints which form each core joint being alternate buttand overlap joints.

GARE'I'H G. SOWRVIILE.

REFERENCES CITED The following references are or record in the file ofthis patent:

UNITED s'rA'rEs PA'I'EN'I'S Number Name Date 523,572 Hassler July 24,1894 1,102,513 Johannesen July 7, 1914 1,365,569 Troy Jan. 11, 19291,933,140 Gakle Oct. 31, 1933 1,935,426 Acly NOV. 14, 1933 2,332,127Annis Oct. 19, 1943 FOREIGN PATENTS Number Country Date 7,856 GreatBritain 1889 106,986 Great Britain June 14, 1917

